Organic EL panels provided with organic electroluminescent elements utilizing the electroluminescence of organic materials have drawn attention in recent years. Organic EL elements emit light by recombining holes injected from the anode and electrons injected from the cathode within a light-emitting layer disposed between these electrodes. Organic EL panels are superior in terms of high contrast and low power consumption, for example, to liquid crystal display devices when used as display panels of thin profile display devices. Organic EL panels are also expected to be used in applications other than display devices, such as lighting.
In order to be used in applications such as display devices, organic EL panels need to emit light of various colors. Organic EL element structures capable of emitting white light are strongly desired. Various organic EL element structures capable of emitting white light have been proposed. For example, an element structure called a tandem mode is known in which multiple organic EL elements are stacked in the vertical direction and are driven by a single power source. In a common tandem mode, each organic EL element emits light of a primary color. Further, another tandem mode is also known in which multiple organic EL elements emitting white light are stacked (for example, see Patent Literature 1).
Other known structures include an element structure in which light-emitting layers of different colors are stacked adjacently (for example, see Patent Literature 2) and an element structure in which two or more luminescent dopant materials with different luminescence peak wavelengths are contained in a single light-emitting layer (for example, see Patent Literature 3).